How to Test a Led Third Brake Light With Continuity Tester
- #1
How do you do a continuity test if the light at the top of the mast is LED ?
- #2
Aurai
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Hello,
You should be able to test the light circuit at the base of your mast or wherever the circuit joins are. There will be a live (red) to the light and a negative (black) return. Sometimes the return negative is shared, but you still test that wire. Then with your continuity tester clip on to cable ends. Guessing you have a multi meter?
If no sign of continuity, you eventually have to get up to the light or bring the mast down!
Good luck, happy if you pm for specific questions or guidance.
CH
- #3
Sandyman
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Its a DIODE. Switch your test leads round?
- #4
lw395
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You may need a higher voltage source than a multimeter, which won't drive any current into a 12V LED bulb.
- #5
prv
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Look upwards and see if the light is on? 
Pete
- #6
Look upwards and see if the light is on?
Pete
- #7
What are you trying to determine? Presumably nothing is shining of any colour? If you want to know if current is flowing but giving no illumination, put a multimeter set to measure current across the switch...
Mike.
- #8
jamie N
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Connect a multimeter to the conductors, all DVM's have variable resistance settings, so try the middle setting. When you test you'll see either open circuit/infinity, or a reading of (perhaps) 1.234 ohms, the numbers aren't really relevant. After taking the 1st reading, reverse your probes and with luck you'll see the other reading. Good luck by the way!
- #9
Or just set your multimeter to the diode test setting.... It'll provide enough forward voltage then....
- #10
prv - that was a classic answer and pragmatic - Thanks.
However, I thought everyone would come back and say YOU CAN'T do a continuity with an LED light in the circuit.
So there you are, I continue to learn.
Thanks, everyone.
Look upwards and see if the light is on?
Pete
- #11
VicS
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- #12
jamie N
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Quite right, but for simplicity of explanation........! Cheers£
- #13
DJE
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Could you use a 12V battery and a bulb in series with the test circuit?
- #14
VicS
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There are only 2 ways .
Apply power at the bottom.
If the light lights all is well.
If it does not then there is a lack of continuity or the lamp has failed. Either way it means a trip to the top:
Short the two wires together at the top , Stay up there while someone checks at the bottom with a meter with a buzzer or with a bulb and battery.
If there is no continuity test each wire individually by shorting to the mast at the top and testing between the bottom ends and the mast .
- #15
lw395
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None of mine will.
At least not for any 12V leds where the current is simply resistor controlled.
Most multimeters are powered by 9V batteries. The LEDs are i strings of 3 with each having a Vf of over 3V. Plus many have a bridge rectifier adding another 1.3V of Vf.
I'd use a 12V current limited supply my self, but 12V with a light bulb in series in case of shorts is a good suggestion.
Source: https://forums.ybw.com/index.php?threads/how-do-you-do-a-continuity-test-with-leds.449609/